show how to change default type for %-sigiled containers

doc/Language/variables.pod

@@ -29,6 +29,27 @@ Examples:
     my @array  = 1, 2, 3;   # Array variable with three elements
     my %hash   = London => 'UK', Berlin => 'Germany';
 
+The default type can be set with C<is>.
+
+    class FailHash is Hash {
+		has Bool $!final = False;
+		multi method AT-KEY ( ::?CLASS:D: Str:D \key ){
+			fail X::OutOfRange.new(:what("Hash key"), :got(key), :range(self.keys)) if $!final && !self.EXISTS-KEY(key);
+			callsame
+		}
+
+		method finalize () {
+			$!final = True
+		}
+    }
+    
+    my %h is FailHash = oranges => "round", bananas => "bendy";
+    say %h<oranges>;
+    # OUTPUT «round␤»
+    %h.finalize;
+    say %h<cherry>;
+    # OUTPUT «Hash key out of range. Is: cherry, should be in (oranges bananas)␤  in method AT-KEY at failhash.p6 line 4 [...]»
+
 Variables without sigils are also possible, see
 L<sigilless variables|#Sigilless variables>.